From 3418ebebfe36e7bcaf380fd3a462b77b59adf1f9 Mon Sep 17 00:00:00 2001
From: Matthew Dillon <dillon@FreeBSD.org>
Date: Wed, 26 Sep 2001 06:54:32 +0000
Subject: [PATCH] Make uio_yield() a global.  Call uio_yield() between chunks
 in vn_rdwr_inchunks(), allowing other processes to gain an exclusive lock on
 the vnode.  Specifically: directory scanning, to avoid a race to the root
 directory, and multiple child processes coring simultaniously so they can
 figure out that some other core'ing child has an exclusive adv lock and just
 exit instead.

This completely fixes performance problems when large programs core.  You
can have hundreds of copies (forked children) of the same binary core all
at once and not notice.

MFC after:	3 days
---
 sys/kern/imgact_aout.c | 4 ++--
 sys/kern/imgact_elf.c  | 4 ++--
 sys/kern/kern_subr.c   | 4 +---
 sys/kern/vfs_vnops.c   | 5 ++++-
 sys/sys/uio.h          | 1 +
 5 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/sys/kern/imgact_aout.c b/sys/kern/imgact_aout.c
index 3ec8f5fbc8de..5a5358193fb4 100644
--- a/sys/kern/imgact_aout.c
+++ b/sys/kern/imgact_aout.c
@@ -269,14 +269,14 @@ aout_coredump(td, vp, limit)
 		error = vn_rdwr(UIO_WRITE, vp, vm->vm_daddr,
 		    (int)ctob(vm->vm_dsize),
 		    (off_t)ctob(UAREA_PAGES + KSTACK_PAGES), UIO_USERSPACE,
-		    IO_UNIT, cred, (int *) NULL, td);
+		    IO_UNIT | IO_DIRECT, cred, (int *) NULL, td);
 	if (error == 0)
 		error = vn_rdwr_inchunks(UIO_WRITE, vp,
 		    (caddr_t) trunc_page(USRSTACK - ctob(vm->vm_ssize)),
 		    round_page(ctob(vm->vm_ssize)),
 		    (off_t)ctob(UAREA_PAGES + KSTACK_PAGES) +
 		        ctob(vm->vm_dsize), UIO_USERSPACE,
-		    IO_UNIT, cred, (int *) NULL, td);
+		    IO_UNIT | IO_DIRECT, cred, (int *) NULL, td);
 	return (error);
 }
 
diff --git a/sys/kern/imgact_elf.c b/sys/kern/imgact_elf.c
index 66a3a3481be2..d7a27baaf500 100644
--- a/sys/kern/imgact_elf.c
+++ b/sys/kern/imgact_elf.c
@@ -802,7 +802,7 @@ elf_coredump(td, vp, limit)
 			error = vn_rdwr_inchunks(UIO_WRITE, vp, 
 			    (caddr_t)php->p_vaddr,
 			    php->p_filesz, offset, UIO_USERSPACE,
-			    IO_UNIT, cred, (int *)NULL, curthread); /* XXXKSE */
+			    IO_UNIT | IO_DIRECT, cred, (int *)NULL, curthread); /* XXXKSE */
 			if (error != 0)
 				break;
 			offset += php->p_filesz;
@@ -966,7 +966,7 @@ elf_corehdr(td, vp, cred, numsegs, hdr, hdrsize)
 
 	/* Write it to the core file. */
 	return vn_rdwr_inchunks(UIO_WRITE, vp, hdr, hdrsize, (off_t)0,
-	    UIO_SYSSPACE, IO_UNIT, cred, NULL, td); /* XXXKSE */
+	    UIO_SYSSPACE, IO_UNIT | IO_DIRECT, cred, NULL, td); /* XXXKSE */
 }
 
 static void
diff --git a/sys/kern/kern_subr.c b/sys/kern/kern_subr.c
index 9f53d2d1f00e..cab78c2015ca 100644
--- a/sys/kern/kern_subr.c
+++ b/sys/kern/kern_subr.c
@@ -55,8 +55,6 @@
 #include <vm/vm_page.h>
 #include <vm/vm_map.h>
 
-static void	uio_yield __P((void));
-
 SYSCTL_INT(_kern, KERN_IOV_MAX, iov_max, CTLFLAG_RD, NULL, UIO_MAXIOV, 
 	"Maximum number of elements in an I/O vector; sysconf(_SC_IOV_MAX)");
 
@@ -381,7 +379,7 @@ phashinit(elements, type, nentries)
 	return (hashtbl);
 }
 
-static void
+void
 uio_yield()
 {
 	struct thread *td;
diff --git a/sys/kern/vfs_vnops.c b/sys/kern/vfs_vnops.c
index b3160b1d9600..2a2bd8308891 100644
--- a/sys/kern/vfs_vnops.c
+++ b/sys/kern/vfs_vnops.c
@@ -338,7 +338,9 @@ vn_rdwr(rw, vp, base, len, offset, segflg, ioflg, cred, aresid, td)
  * Package up an I/O request on a vnode into a uio and do it.  The I/O
  * request is split up into smaller chunks and we try to avoid saturating
  * the buffer cache while potentially holding a vnode locked, so we 
- * check bwillwrite() before calling vn_rdwr()
+ * check bwillwrite() before calling vn_rdwr().  We also call uio_yield()
+ * to give other processes a chance to lock the vnode (either other processes
+ * core'ing the same binary, or unrelated processes scanning the directory).
  */
 int
 vn_rdwr_inchunks(rw, vp, base, len, offset, segflg, ioflg, cred, aresid, td)
@@ -367,6 +369,7 @@ vn_rdwr_inchunks(rw, vp, base, len, offset, segflg, ioflg, cred, aresid, td)
 			break;
 		offset += chunk;
 		base += chunk;
+		uio_yield();
 	} while (len);
 	if (aresid)
 		*aresid += len;
diff --git a/sys/sys/uio.h b/sys/sys/uio.h
index 48f6c97bce26..eec95a285ef3 100644
--- a/sys/sys/uio.h
+++ b/sys/sys/uio.h
@@ -84,6 +84,7 @@ struct uio {
 
 struct vm_object;
 
+void	uio_yield __P((void));
 int	uiomove __P((caddr_t, int, struct uio *));
 int	uiomoveco __P((caddr_t, int, struct uio *, struct vm_object *));
 int	uioread __P((int, struct uio *, struct vm_object *, int *));